This invention relates to an engine control strategy and system and more particularly to an improved control strategy and system for direct cylinder injected, two cycle, internal combustion engines.
The advantages afforded by the simplicity of two cycle engines is well recognized. Also, the ability of these engines to produce greater horsepower per displacement than four cycle engines due to their firing every cycle of rotation is acknowledged. However, because of the overlap in the scavenging and exhaust cycles and other factors, environmental concerns are making the use of two cycle engines more difficult.
One way in which the performance of a two cycle engine can be significantly improved and, at the same time, the fuel economy and exhaust emission control can be improved is through the use of direct cylinder fuel injection. With this type of injection system, fuel is injected directly into the combustion chamber for combustion therein. By utilizing direct cylinder injection, it may be possible to obtain stratification of the charge and, accordingly, exhaust emission and fuel economy improvement.
However, the fact that exhaust port is opened during a portion of the intake or scavenging cycle gives rise to the possibility that injected fuel can be swept out of the exhaust port. Therefore, it has generally been the practice to inject the fuel very late in the compression cycle and oftentimes fuel injection begins immediately after the exhaust port is closed and before the piston has reached its top dead center position. Such a practice will ensure that fuel does not pass out of the exhaust port.
However, this late injection of fuel, particularly under lower speed and load conditions gives rise to a very great difficulty in obtaining proper mixing in the combustion chamber. That is, when the fuel is injected late, there is less turbulence and airflow in the combustion chamber. This result in poor mixing and incomplete combustion.
It is, therefore, a principal object of this invention to provide an improved direct injected two cycle engine and operating strategy.
It is a further object of this invention to provide a fuel control arrangement for a direct injected two cycle engine wherein the timing of the fuel injection is governed so as to ensure that fuel will not pass out of the exhaust port but also so that the fuel is well mixed in the combustion chamber before ignition timing.
To improve the operation of direct injected, two cycle engines, a system has been proposed by us that is described in the co-pending application entitled, "Control for Direct Injected Two Cycle Engine", Ser. No. 09/188,953, Filed Nov. 10, 1998, now U.S. Pat. No. 6,058,908 and assigned to the Assignee hereof. As disclosed therein the injection initiation and duration is controlled so as to minimize the likelihood of fuel escaping from the exhaust port while still obtaining maximum power output. In accordance with that arrangement, the initial fuel injection is begun at a point when the exhaust port is still open but at a time wherein the fuel injected will not reach the exhaust port during the time when the exhaust port is still open. Basically, injection is done while the exhaust port is open rather than delaying it until after it closes as with more conventional methodologies.
In order to achieve this result and still avoid the likelihood that unburned fuel may pass out of the exhaust port, further improvements are believed to be possible. For example, the premise of our aforenoted pending application is based upon injecting so that the duration will end at a time when the first injected fuel will not yet have reached the exhaust port before it has closed. However, it has been discovered that factors may be present in the combustion chamber that can effect the time at which this event occurs.
It is, therefore, a principle object of this invention to provide an improved engine control strategy and system for a direct injected two-cycle engine.
It is a further object of this invention to provide an improved engine control strategy and system for a direct injected two-cycle engine wherein in-cylinder conditions are considered in determining the injection timing.
In conjunction with direct injection in the cylinder, it is also important that the fuel be injected at such a time and for such a duration that it will well mix in the combustion chamber. Unless the fuel is well mixed with the surrounding air, the particles may be too large to completely burn during the combustion cycle.
It is, therefore, a still further object of this invention to provide an improved fuel injection control and method therefor that will improve the efficiency of two-cycle engines while still maintaining good exhaust emission control.